Enter "The Dragon Lady"
I own a high horse friction machine. Dual 2.2hp 43cc Mitsubishi engines, one on each tire. Twin ADA S1 expansion pipes, WYK-58 Walbro carbs to be installed next.
Maybe tw0 5hp GP460 engines on friction drive in the future. Shhhh
If using only one engine, install it on rear tire. Handling at walking speed suffers with front drive.
A front engine mount might be difficult to install if you have a suspension fork.
Be sure to route the exhaust to the side, not in your face.
The front expansion pipe's exhaust blew directly in my face. I rerouted the fumes with a 39" long rubber exhaust tube. The smoke exits below the crankset. The tubing muffles the sound so well that I disconnected and removed the silencer.
Old cruiser? To go fast you need to stop fast, often and with no brake fade.
I have a girlie cruiser frame with coaster brake as well as front and rear side-pull vee-brakes.
Positives include the simplest drive with no chain breakage or alignment.
Negatives are slipping tire engagement on wet roads and tire wear. Certain friction kits have rollers which are a bear to swap out.